Possible Clues:

• To Kill a Mockingbird screenwriter
• Tender Mercies penner Horton
• Civil War scholar Shelby
• "Shiloh" author Shelby
• Author of the 3,000-page "The Civil War: A Narrative"
• "The Trip to Bountiful" author
• Civil War historian
• 'The Young Man From Atlanta' Pulitzer winner, 1995
• 'Shiloh' novelist Shelby